1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing a non-volatile semiconductor memory for storing a read channel parameter calibrated for the disk drive used to recover a disk channel parameter.
2. Description of the Prior Art
As shown in FIG. 1A, a disk drive typically comprises a disk 2 for storing data and a head 4 actuated radially over the disk 2 for writing data to and reading data from the disk 2. The head 4 is connected to an actuator arm 6 which is rotated about a pivot 8 by a voice coil motor (not shown). The data to be written to the disk 2 modulates operation of the head 4 in order to write a series of transitions (magnetic or optical) on the disk surface along the centerline of typically concentric or spiral tracks. When reading data recorded on the disk 2, a special read channel circuit is employed to detect an estimated data sequence from a read signal emanating from the head 4.
An example format for a magnetic disk 2A is illustrated in FIG. 1B as comprising a plurality of concentric tracks 10, wherein each concentric track 10 is partitioned into a plurality of data sectors 12. An example format of a data sector 12 recorded on the magnetic disk 2A is shown in FIG. 1C as comprising a preamble 20, a sync mark 22, a data field 24 and appended ECC symbols 26. The preamble 20 allows the read channel circuit to acquire the appropriate timing and gain information from the read signal before reading the data field 24, and the sync mark 22 demarks the beginning of the data field 24 so that it can be symbol synchronized. The appended ECC symbols 26 are used to detect and correct errors in an estimated data sequence detected by the read channel circuit.
Referring again to FIG. 1B, a plurality of the concentric tracks 10 are banded together to form at least an inner zone 14 and an outer zone 16, and at least one of the sectors 12 is a reserved sector for storing calibrated data-sector channel parameters. The magnetic disk 2A is partitioned into a plurality of zones in order to achieve a more constant linear bit density from the inner diameter to outer diameter tracks, thereby exploiting the maximum storage capacity of the disk by increasing the data rate from the inner to outer diameter zones. The changing data rate between zones, however, militates the need to calibrate the read channel in order to operate more optimally in each zone. Thus, disk drives typically reserve at least one sector for storing calibrated data-sector channel parameters calibrated during manufacturing. When the disk drive is powered on during normal operation, the calibrated data-sector channel parameters are read from the reserved sector(s) and used to program read channel circuit depending on the radial location of the head 4 with respect to the disk 2.
Programming the read channel circuit with calibrated channel parameters enables higher linear recording densities leading to an increase in the disk drive""s overall storage capacity. However, when the disk drive is powered on initially, the calibrated channel parameters for reading the reserved sector(s) are unknown, and therefore the read channel circuit is initially programmed with nominal channel parameters. The nominal channel parameters, determined during manufacturing, are typically set to values which should work well for a family of disk drives on average. However, due to manufacturing process variations (e.g., variations in head sensitivity, fly height, media, embedded servo bursts, etc.), a percentage of the disk drives will not be able to read the reserved sector(s) using the nominal channel parameters. If the reserved sector(s) cannot be read, the disk drive may be discarded even though it may otherwise fall within acceptable tolerances. This leads to an undesirable reduction in manufacturing yield.
There is, therefore, a need to improve a disk drive""s ability to read calibrated data-sector channel parameters stored in reserved sector(s) when the disk drive is powered on, thereby improving the manufacturing yield.
The present invention may be regarded as a disk drive comprising a disk with a reserved sector for storing a data-sector channel parameter, and a data sector for storing data. The disk drive further comprises a read channel circuit comprising a parameter register, and a non-volatile semiconductor memory (NSM) storing a reserved-sector channel parameter that is selected by using a parameter calibration procedure performed for the disk drive. A disk controller retrieves the reserved-sector channel parameter stored in the NSM, programs the parameter register with the retrieved reserved-sector channel parameter in order to configure the read channel circuit to recover the data-sector channel parameter stored in the reserved sector, and programs the parameter register with the recovered data-sector channel parameter so that the read channel circuit is configured to recover the data stored in the data sector.
The present invention may also be regarded as a method of manufacturing a disk drive comprising a head for writing data to and reading data from a disk, a non-volatile semiconductor memory (NSM), and a read channel for detecting an estimated data sequence from a read signal emanating from the head. A reserved-sector channel parameter is calibrated for recovering a calibrated data-sector channel parameter stored in a reserved sector. The data-sector channel parameter is calibrated for recovering data from a data sector. The calibrated data-sector channel parameter is written to the reserved sector, and the calibrated reserved-sector channel parameter is stored in the NSM.
The present invention may also be regarded as a method of reading data recorded in a disk drive comprising a head for writing data to and reading data from a disk, a non-volatile semiconductor memory (NSM), and a read channel for detecting an estimated data sequence from a read signal emanating from the head. The read channel is programmed with calibrated reserved sector read channel parameters stored in the NSM. A calibrated data-sector channel parameter is read from the reserved sector and stored in random access memory (RAM). The read channel is programmed with the calibrated data-sector channel parameter stored in RAM, and data is then read from a data sector.